U.S. patent application number 14/327759 was filed with the patent office on 2015-01-15 for system and method for cooling an aircraft fuel cell system.
The applicant listed for this patent is Airbus Operations GmbH. Invention is credited to Guido Klewer, Hauke Peer Luedders, Sebastian Mock, Christian Mueller.
Application Number | 20150017559 14/327759 |
Document ID | / |
Family ID | 52107299 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150017559 |
Kind Code |
A1 |
Klewer; Guido ; et
al. |
January 15, 2015 |
System and method for cooling an aircraft fuel cell system
Abstract
A system for cooling an aircraft fuel cell system comprising a
first cooling circuit thermally coupled to a first fuel cell, to
remove thermal energy generated by the first fuel cell during
operation from the first fuel cell, and a first heat exchanger
arranged in the first cooling circuit and adapted to transfer
thermal energy, removed from the first fuel cell via the first
cooling circuit, to the aircraft surroundings. The system comprises
a second cooling circuit thermally coupled to a second fuel cell,
to remove thermal energy generated by the second fuel cell during
operation from the second fuel cell, and a second heat exchanger
arranged in the second cooling circuit and adapted to transfer
thermal energy, removed from the second fuel cell via the second
cooling circuit, to the aircraft surroundings. The first cooling
circuit is thermally couplable to the second cooling circuit.
Inventors: |
Klewer; Guido; (Hamburg,
DE) ; Luedders; Hauke Peer; (Hamburg, DE) ;
Mock; Sebastian; (Hamburg, DE) ; Mueller;
Christian; (Hamburg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Airbus Operations GmbH |
Hamburg |
|
DE |
|
|
Family ID: |
52107299 |
Appl. No.: |
14/327759 |
Filed: |
July 10, 2014 |
Current U.S.
Class: |
429/435 |
Current CPC
Class: |
H01M 2250/20 20130101;
H01M 8/04067 20130101; H01M 8/04701 20130101; Y02T 90/40 20130101;
H01M 8/04708 20130101; B64D 2041/005 20130101; Y02E 60/50
20130101 |
Class at
Publication: |
429/435 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 11, 2013 |
DE |
102013213573.4 |
Claims
1. A system for cooling an aircraft fuel cell system comprising: a
first cooling circuit thermally coupled to a first fuel cell, in
order to remove thermal energy generated by the first fuel cell
during operation from the first fuel cell, a first heat exchanger
arranged in the first cooling circuit and adapted to transfer
thermal energy, removed from the first fuel cell via the first
cooling circuit, to the aircraft surroundings, a second cooling
circuit thermally coupled to a second fuel cell, in order to remove
thermal energy generated by the second fuel cell during operation
from the second fuel cell, and a second heat exchanger arranged in
the second cooling circuit and adapted to transfer thermal energy,
removed from the second fuel cell via the second cooling circuit,
to the aircraft surroundings, the first cooling circuit being
thermally couplable to the second cooling circuit.
2. The system according to claim 1, wherein at least one of the
first and the second heat exchanger is integrated into an outer
skin of the aircraft, is adapted to be flowed through with ambient
air, and is provided with a plurality of cooling ribs at least in a
region of an outer surface facing away from an interior of the
aircraft.
3. The system according to claim 1, wherein the first cooling
circuit is thermally couplable to the second cooling circuit via a
third heat exchanger.
4. The system according to claim 3, wherein the third heat
exchanger is thermally couplable to a device to be heated.
5. The system according to claim 4, wherein the device to be heated
is a fuel which flows through a fuel supply line which connects a
fuel tank to at least one of the first and the second fuel
cell.
6. The system according to claim 3, wherein in the third heat
exchanger, at least one tube forming a section of the first cooling
circuit is connected in a heat-transferring manner to at least one
tube forming a section of the second cooling circuit.
7. The system according to claim 6, wherein in the third heat
exchanger, the tubes connected in a heat-transferring manner to one
another and forming a section of the first cooling circuit and a
section of the second cooling circuit are arranged in a receiving
space, through which fuel to be heated can flow.
8. A method for cooling an aircraft fuel cell system comprising the
steps: removing thermal energy from a first fuel cell by means of a
first cooling circuit which is thermally coupled to the first fuel
cell, transferring the thermal energy, removed from the first fuel
cell via the first cooling circuit, to the aircraft surroundings by
means of a first heat exchanger arranged in the first cooling
circuit, removing thermal energy from a second fuel cell by means
of a second cooling circuit which is thermally coupled to the
second fuel cell, transferring the thermal energy, removed from the
second fuel cell via the second cooling circuit, to the aircraft
surroundings by means of a second heat exchanger arranged in the
second cooling circuit, the first cooling circuit being thermally
coupled to the second cooling circuit.
9. The method according to claim 8, wherein, when an aircraft
equipped with the aircraft fuel cell system is in flight or is on
the ground, the first and the second fuel cell are operated at
different powers and the thermal energy which is generated by the
fuel cell operated at a higher power is removed via the first and
the second cooling circuit and transferred by means of the first
and the second heat exchanger to the aircraft surroundings.
10. The method according to claim 9, wherein, when the aircraft
equipped with the aircraft fuel cell system is in flight, the
thermal energy generated by the first or the second fuel cell is
transferred to the aircraft surroundings exclusively via a
plurality of cooling ribs which are provided in the region of an
outer surface, facing away from an interior of the aircraft, of the
first and the second heat exchanger.
11. The method according to claim 8, wherein the first cooling
circuit is thermally coupled to the second cooling circuit via a
third heat exchanger.
12. The method according to claim 11, wherein the third heat
exchanger is thermally coupled to a device to be heated.
13. The method according to claim 12, wherein the device to be
heated is a fuel which flows through a fuel supply line which
connects a fuel tank to at least one of the first and the second
fuel cell.
14. The method according to claim 11, wherein, in the third heat
exchanger, at least one tube forming a section of the first cooling
circuit is connected in a heat-transferring manner to at least one
tube forming a section of the second cooling circuit.
15. The method according to claim 14, wherein, in the third heat
exchanger, the tubes connected in a heat-transferring manner to one
another and forming a section of the first cooling circuit and a
section of the second cooling circuit are arranged in a receiving
space, through which fuel to be heated flows.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit of the German patent
application No. 10 2013 213 573.4 filed on Jul. 11, 2013, the
entire disclosures of which are incorporated herein by way of
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a system and a method for
cooling a fuel cell system installed on board an aircraft.
[0003] Fuel cell systems enable low-emission, highly efficient
generation of electric current. For this reason, efforts are
currently being made to use fuel cell systems to generate
electrical energy in various mobile applications, such as for
example in automotive engineering, in shipping or in aviation. It
is, for example, conceivable in an aircraft to replace the
generators, which are currently used to supply power on board and
are driven by the main engines or the auxiliary turbine, with a
fuel cell system. A fuel cell system, moreover, could also be used
to supply the aircraft with emergency power and replace the ram air
turbine hitherto used as an emergency power system. Besides
electrical energy, a fuel cell during operation generates thermal
energy, which has to be removed from the fuel cell with the aid of
a cooling system in order to prevent overheating of the fuel cell.
A fuel cell used in an aircraft, for example for the on-board power
supply, has to be designed in such a way that it is capable of
meeting the demand for electrical energy. However, a fuel cell that
has a high capacity with regard to generating electrical energy,
also generates, due to the efficiency, corresponding thermal
energy, and therefore has a corresponding cooling requirement.
[0004] In principle, a fuel cell system used on board an aircraft
can be cooled in various ways. For example, DE 10 2009 013 159 A1
or WO 2010/105744 A2 describes a cooler which is integrated into an
outer skin of the aircraft and through which ambient air can flow
in order to remove waste heat generated by a fuel cell system to
the aircraft surroundings.
[0005] By contrast, DE 10 2009 048 394 A1 proposes coupling a
cooling circuit, which removes thermal energy generated by a fuel
cell system during operation from the fuel cell system, thermally
to a fuel tank, in order to utilize fuel held in the fuel tank as a
heat sink for cooling the fuel cell system.
[0006] Finally, from DE 10 2007 060 428 B3 or WO 2009/077048 A1
there is known an evaporative cooling system for cooling a fuel
cell system, in which a cooling medium is converted from the liquid
to the gaseous state of matter by the thermal energy generated
during operation of the fuel cell system.
SUMMARY OF THE INVENTION
[0007] An object on which the invention is based is to provide an
efficient system and method for cooling an aircraft fuel cell
system.
[0008] A system for cooling an aircraft fuel cell system comprises
a first cooling circuit which is thermally coupled to a first fuel
cell, in order to remove thermal energy generated by the first fuel
cell during operation from the first fuel cell. A liquid or a
gaseous coolant may flow through the first cooling circuit.
Furthermore, it is conceivable to circulate in the first cooling
circuit a two-phase coolant, i.e., a coolant which is converted
from liquid to the gaseous state by the thermal energy of the first
fuel cell and subsequently condensed out again in a condenser.
Furthermore, the system comprises a first heat exchanger arranged
in the first cooling circuit. The first heat exchanger is adapted
to transfer thermal energy, removed from the first fuel cell via
the first cooling circuit, to the aircraft surroundings. In the
first cooling circuit, the first heat exchanger therefore serves as
a heat sink for the waste heat generated by the first fuel cell
during operation.
[0009] The system for cooling an aircraft fuel cell system
furthermore comprises a second cooling circuit which is thermally
coupled to a second fuel cell, in order to remove thermal energy
generated by the second fuel cell during operation from the second
fuel cell. Similarly to the first cooling circuit, the second
cooling circuit may, as required, also be operated with a liquid, a
gaseous or a two-phase coolant. A second heat exchanger is arranged
in the second cooling circuit. The second heat exchanger is adapted
to transfer thermal energy, removed from the second fuel cell via
the second cooling circuit, to the aircraft surroundings and
therefore to serve as a heat sink for the thermal energy generated
by the second fuel cell during operation.
[0010] The aircraft fuel cell system to be cooled by means of the
cooling system according to the invention therefore comprises two
fuel cells which generate heat during operation and which are
cooled by two cooling circuits formed, in principle, separately
from one another. The fuel cells are preferably configured in the
form of fuel cell stacks which comprise a plurality of individual
cells arranged one above the other. The first cooling circuit is,
however, thermally couplable to the second cooling circuit.
[0011] A redundant cooling of the two fuel cells of the aircraft
fuel cell system is ensured by the thermal coupling of the two
cooling circuits, since in the event of a failure of one cooling
circuit, the cooling circuit which is still functional can be used
to ensure an emergency cooling of both fuel cells of the aircraft
fuel cell system, for example until the operation of the fuel cell,
cooled by the failed cooling circuit, has been properly ended.
Furthermore, in a system in which the two fuel cells are operated
at different power, the cooling energy provided by the cooling
circuits can be optimally distributed to the fuel cells to be
cooled, since excess cooling energy which is provided by the
cooling circuit which is assigned to the fuel cell operated at
lower power, can be used to cool the fuel cell operated at higher
power.
[0012] If desired, the system for cooling an aircraft fuel cell
system may also comprise more than two cooling circuits and/or more
than two fuel cells. A separate cooling circuit may be assigned to
each fuel cell. Alternatively, however, it is also conceivable to
cool two or more fuel cells by a common cooling circuit or to use
more than one cooling circuit to cool one fuel cell.
[0013] Today's operating scenarios assume that when an aircraft
equipped with the system for cooling an aircraft fuel cell system
is on the ground, both fuel cells of the aircraft fuel cell system
are active, i.e., generate electrical energy and therefore waste
heat, whereas when the aircraft is in flight, by contrast, only one
of the two fuel cells of the aircraft fuel cell system is operated.
Furthermore, it is conceivable to operate only one fuel cell when
the aircraft is on the ground, for example if the electrical energy
generated by one fuel cell is sufficient to provide the energy
required on board the aircraft. Owing to the thermal coupling of
the two cooling circuits, the cooling system according to the
invention makes it possible, when the aircraft equipped with the
aircraft fuel cell system is in flight or is on the ground with
only one active fuel cell, to use both cooling circuits for cooling
the active fuel cell. As a result, an effective and efficient
cooling of the active fuel cell is made possible. Furthermore,
owing to the thermal coupling of the two cooling circuits, a
freezing of the coolant in a cooling circuit can be prevented even
when the fuel cell to be cooled by means of the cooling circuit is
inactive and therefore does not generate any thermal energy.
[0014] The first heat exchanger arranged in the first cooling
circuit may be integrated into an outer skin of the aircraft and
may be adapted to be flowed through with ambient air. Furthermore,
the first heat exchanger may be provided with a plurality of
cooling ribs at least in the region of an outer surface facing away
from an interior of the aircraft. Similarly, the second heat
exchanger may be integrated into an outer skin of the aircraft, may
be adapted to be flowed through with ambient air, and may be
provided with a plurality of cooling ribs at least in the region of
an outer surface facing away from an interior of the aircraft. The
cooling ribs ensure in particular an increase of the
heat-transferring surface of the first and/or the second heat
exchanger and therefore an improvement of the heat-transfer
capacity of the first and/or the second heat exchanger.
[0015] The ambient air flow led through the first and/or the second
heat exchanger is normally a forced flow which is induced by a
suitable conveying device, for example a fan or the like, arranged,
for example, in the interior of an aircraft equipped with the
system for cooling an aircraft fuel cell system. When the aircraft
is on the ground, the transfer of the thermal energy, generated by
the fuel cells of the aircraft fuel cell system, to the aircraft
surroundings is effected predominantly by the ambient air flow led
through the first and/or the second heat exchanger. By contrast,
when the aircraft is in flight, the cooling ribs provided on an
outer surface of the first and/or the second heat exchanger
substantially ensure the heat transfer to the aircraft
surroundings. When using a conventional cooling system for cooling
the fuel cells of the aircraft fuel cell system, however, at least
a small ambient air flow through the first and/or the second heat
exchanger is generally also required when the aircraft is in
flight, in order to ensure proper cooling of the fuel cells.
[0016] In contrast to this, when an aircraft equipped with the
system for cooling an aircraft fuel cell system according to the
invention is in flight, the thermal coupling of the two cooling
circuits enables the use of both cooling circuits and therefore
both heat exchangers arranged in the cooling circuits for cooling
the fuel cell active when the aircraft is in flight. In the cooling
system according to the invention, the cooling capacity produced by
the cooling ribs of the heat exchangers is therefore sufficient to
ensure proper cooling of the active fuel cell. An additional flow
of ambient air through the first and/or the second heat exchanger
can therefore be dispensed with.
[0017] Dispensing with an additional flow of ambient air through
the first and/or the second heat exchanger makes it possible to
reduce the aerodynamic drag and therefore the fuel consumption of
an aircraft equipped with the system for cooling an aircraft fuel
cell system according to the invention. Furthermore, the aircraft
no longer has to be equipped with special air inlets which, when
the aircraft is in flight, enable an ambient air flow through the
first and/or the second heat exchanger, but increase the
aerodynamic drag and therefore the fuel consumption of the aircraft
in flight. It is also possible to dispense with flaps controlling
the air flow through the air inlets, as well as actuators required
for the actuation of the flaps. As a result, the system complexity
is reduced and the reliability of the system as a whole is
increased.
[0018] In principle, it is conceivable to design the first and the
second cooling circuit of the system for cooling a fuel cell system
such that a direct coupling of the first to the second cooling
circuit is possible. For this purpose, provision may be made, for
example, for corresponding connecting lines and valves which, if
required, establish a fluid-conducting connection between the first
and the second cooling circuit. Such a configuration of the thermal
coupling between the first and the second cooling circuit, however,
is only appropriate if the same coolant circulates in the first and
the second cooling circuit. Alternatively to this, the first
cooling circuit may be thermally couplable to the second cooling
circuit via a third heat exchanger. As a result, the first and the
second cooling circuit can still be formed separately from one
another, with the result that, for example in the event of a leak
in a cooling circuit, the amount of coolant which escapes is
advantageously limited. Furthermore, the cooling circuits can be
operated, if desired, also with different coolants.
[0019] The third heat exchanger may be thermally couplable to a
device to be heated. The waste heat generated by the first and the
second fuel cell during operation can then, if required, be used
particularly efficiently for heating the device to be heated,
before excess thermal energy is removed to the aircraft
surroundings via the first and the second heat exchanger.
Preferably, the third heat exchanger is then embodied in the form
of a 3-way heat exchanger which is adapted both to bring the two
cooling circuits of the system for cooling a fuel cell system into
thermal contact with one another and to ensure a thermal coupling
of the two cooling circuits to the device to be heated.
[0020] In a preferred embodiment of the system for cooling a fuel
cell system, the device to be heated is a fuel which flows through
a fuel supply line which connects a fuel tank to the first and/or
the second fuel cell. The fuel tank may be configured in the form
of a hydrogen tank. In particular, the hydrogen tank may be a
liquid hydrogen tank, thus a hydrogen tank which is adapted to
store the hydrogen, to be supplied to the fuel cells of the
aircraft fuel cell system as fuel, in a space-saving manner in the
liquid state of matter. The third heat exchanger coupling the first
to the second cooling circuit can then be advantageously used to
heat up and optionally evaporate the fuel stored in the fuel tank
before being supplied to the first and/or the second fuel cell.
This enables a particularly efficient use of the waste heat
generated by the first and the second fuel cell during operation
within the system as a whole.
[0021] In the third heat exchanger, at least one tube which forms a
section of the first cooling circuit may be connected in a
heat-transferring manner to at least one tube which forms a section
of the second cooling circuit. In particular, the third heat
exchanger may be embodied in the form of a tube-bundle heat
exchanger, in which a tube bundle forming a section of the first
cooling circuit is connected in a heat-transferring manner to a
tube bundle forming a section of the second cooling circuit. In
particular, tubes assigned to the first cooling circuit and tubes
assigned to the second cooling circuit may be connected to one
another in a thermally conducting manner in each case in pairs in
the third heat exchanger. A thermally conducting connection between
the tubes may be produced, for example, by a soldered connection,
an adhesively bonded connection or a welded connection.
[0022] Furthermore, in the third heat exchanger, the tubes
connected in a heat-transferring manner to one another and forming
a section of the first cooling circuit and a section of the second
cooling circuit may be arranged in a receiving space. Fuel to be
heated may flow through the receiving space, i.e., the receiving
space can form a section of the fuel supply line connecting the
fuel tank to the first and/or the second fuel cell. As a result, a
direct heat transfer may be produced from the tubes which form a
section of the first cooling circuit and the tubes which form a
section of the second cooling circuit to the fuel to be heated
flowing around the tubes in the receiving space.
[0023] In a method for cooling an aircraft fuel cell system,
thermal energy is removed from a first fuel cell by means of a
first cooling circuit which is thermally coupled to the first fuel
cell. The thermal energy removed from the first fuel cell via the
first cooling circuit is transferred to the aircraft surroundings
by means of a first heat exchanger arranged in the first cooling
circuit. Thermal energy is removed from a second fuel cell by means
of a second cooling circuit which is thermally coupled to the
second fuel cell. The thermal energy removed from the second fuel
cell via the second cooling circuit is transferred to the aircraft
surroundings by means of a second heat exchanger arranged in the
second cooling circuit. The first cooling circuit is thermally
coupled to the second cooling circuit.
[0024] When an aircraft equipped with the aircraft fuel cell system
is in flight or is on the ground, the first and the second fuel
cell may be operated at different power. For example, only the
first or the second fuel cell may be operated. The thermal energy
which is generated by the fuel cell operated at higher power may be
removed via the first and the second cooling circuit and
transferred by means of the first and the second heat exchanger to
the aircraft surroundings.
[0025] When the aircraft equipped with the aircraft fuel cell
system is in flight, the thermal energy generated by the first or
the second fuel cell is transferred to the aircraft surroundings
preferably exclusively via a plurality of cooling ribs which are
provided in the region of an outer surface, facing away from an
interior of the aircraft, of the first and the second heat
exchanger.
[0026] The first cooling circuit is preferably thermally coupled to
the second cooling circuit via a third heat exchanger.
[0027] The third heat exchanger may furthermore be thermally
coupled to a device to be heated.
[0028] The device to be heated may, for example, be a fuel which
preferably flows through a fuel supply line which connects a fuel
tank to the first and/or the second fuel cell.
[0029] In the third heat exchanger, at least one tube forming a
section of the first cooling circuit may be connected in a
heat-transferring manner to at least one tube forming a section of
the second cooling circuit.
[0030] In the third heat exchanger, the tubes connected in a
heat-transferring manner to one another and forming a section of
the first cooling circuit and a section of the second cooling
circuit may be arranged in a receiving space. Preferably fuel to be
heated flows through the receiving space.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Preferred embodiments of the invention will now be explained
in more detail with reference to the appended schematic drawings,
of which
[0032] FIG. 1 shows a schematic representation of a first
embodiment of a system for cooling an aircraft fuel cell
system,
[0033] FIG. 2 shows a schematic representation of a second
embodiment of a system for cooling an aircraft fuel cell system,
and
[0034] FIG. 3 shows a cross-sectional representation of a heat
exchanger used in the system for cooling an aircraft fuel cell
system according to FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] FIG. 1 shows a system 10 which serves to supply an aircraft
fuel cell system 12 provided on board an aircraft with cooling
energy. The cooling system 10 comprises a first cooling circuit 14
which is thermally coupled to a first fuel cell 16, in order to
remove thermal energy generated by the first fuel cell 16 during
operation from the first fuel cell 16. A liquid or gaseous coolant
can be circulated in the first cooling circuit 14 by means of a
first conveying device 18. Furthermore, it is conceivable to
circulate in the first cooling circuit 14 a two-phase coolant,
i.e., a coolant which is converted from liquid to the gaseous state
by the thermal energy of the first fuel cell and subsequently
condensed out again in a condenser. If the first cooling circuit 14
is operated with a coolant with phase transition, a throttle valve
(not illustrated specifically in FIG. 1) can be arranged in the
first cooling circuit 14. For example, the throttle valve can be
arranged in the first cooling circuit 14 downstream of the first
fuel cell 16. Depending on the state of matter of the coolant
flowing through the first cooling circuit 14 in the region of the
first conveying device 18, the first conveying device 18 can be
configured, for example, in the form of a pump or in the form of a
fan.
[0036] Furthermore, the system 10 comprises a first heat exchanger
20 which is arranged in the first cooling circuit 14 and serves to
transfer thermal energy, removed from the first fuel cell 16 via
the first cooling circuit 14, to the aircraft surroundings. The
first heat exchanger 20 is configured in the form of an outer-skin
heat exchanger integrated into an outer skin of the aircraft and is
provided with a plurality of cooling ribs on an outer surface
facing away from an interior of the aircraft. Moreover, ambient air
can flow through the first heat exchanger 20, i.e., the first heat
exchanger 20 has a plurality of cooling channels, through which
ambient air can flow. The ambient air flow led through the first
heat exchanger 20, if required, is a forced flow which is induced
by a suitable conveying device, for example a fan or the like,
arranged in the interior of the aircraft equipped with the system
10 for cooling an aircraft fuel cell system 12.
[0037] The system 10 for cooling an aircraft fuel cell system 12
furthermore comprises a second cooling circuit 22 which is
thermally coupled to a second fuel cell 24, in order to remove
thermal energy generated by the second fuel cell 24 during
operation from the second fuel cell 24. Similarly to the first
cooling circuit 14, the second cooling circuit 22 can, as required,
also be operated with a liquid, a gaseous or a two-phase coolant
which is conveyed through the second cooling circuit 22 by a second
conveying device 26 configured in the form of a pump or in the form
of a fan. If the second cooling circuit 22 is operated with a
coolant with phase transition, a throttle valve (not illustrated
specifically in FIG. 1) can be arranged in the second cooling
circuit 22. For example, the throttle valve can be arranged in the
second cooling circuit 22 downstream of the second fuel cell 24. A
second heat exchanger 28 arranged in the second cooling circuit 14
serves to transfer thermal energy, removed from the second fuel
cell 24 via the second cooling circuit 22, to the aircraft
surroundings.
[0038] Similarly to the first heat exchanger 20, the second heat
exchanger 28 is also configured in the form of an outer-skin heat
exchanger integrated into an outer skin of the aircraft and is
provided with a plurality of cooling ribs on an outer surface
facing away from an interior of the aircraft. Moreover, ambient air
can flow through the second heat exchanger 28, as in the first heat
exchanger 20, i.e., the second heat exchanger 28 likewise has a
plurality of cooling channels, through which ambient air can flow.
The conveying device serving to convey ambient air through the
first heat exchanger 20 can be adapted, if required, also to induce
a forced ambient air flow through the second heat exchanger 28.
Alternatively to this, however, a separate conveying device for
conveying ambient air through the second heat exchanger 28 may also
be present.
[0039] The aircraft fuel cell system 12 to be cooled by means of
the cooling system 10 therefore comprises two fuel cells 16, 24
which generate heat during operation and which are cooled by the
two cooling circuits 14, 22 formed, in principle, separately from
one another. The first cooling circuit 14 can, however, be
thermally coupled to the second cooling circuit 22, so that a heat
transfer between the two cooling circuits 14, 22 is possible. In
particular, the first cooling circuit 14 can be thermally coupled
to the second cooling circuit 22 via a third heat exchanger 30. In
principle, it is conceivable always to lead the coolant, flowing
through the first and the second cooling circuit 14, 22, through
the third heat exchanger 30 and thereby establish a permanent
thermal coupling of the cooling circuits 14, 22. Alternatively to
this, however, it is also possible to equip the system 10 with
corresponding valves and corresponding bypass lines which make it
possible to lead the coolant, circulating in the first and/or the
second cooling circuit 14, 22, selectively either through the third
heat exchanger 30 or past the third heat exchanger 30. Such a
configuration of the system 10 enables a merely temporary thermal
coupling of the cooling circuits 14, 22.
[0040] In the following, the operation of the system 10 for cooling
an aircraft fuel cell system 12 is explained in more detail. When
an aircraft equipped with the system 10 is on the ground, both fuel
cells 16, 24 of the aircraft fuel cell system 12 are active, i.e.,
both fuel cells 16, 24 of the aircraft fuel cell system 12 generate
electrical energy and therefore waste heat. The waste heat
generated by the fuel cells 16, 24 is removed in each case from the
fuel cells 16, 24 via the corresponding cooling circuits 14, 22
assigned to the fuel cells 16, 24 and is removed to the aircraft
surroundings via the heat exchangers 20, 28 arranged in the cooling
circuits 14, 22. In order to ensure proper heat removal from the
fuel cells 16, 24 of the aircraft fuel cell system 12 when the
aircraft is on the ground, in particular at high ambient
temperatures, a forced ambient air flow through the first and the
second heat exchanger 20, 28 is induced by the conveying device(s)
provided in the interior of the aircraft.
[0041] If a thermal coupling is permanently provided between the
cooling circuits 14, 22 of the cooling system 10 or is actively
established, for example by suitable control of corresponding
valves, a redundant cooling of the two fuel cells 16, 24 of the
aircraft fuel cell system 12 is ensured by the thermal coupling of
the cooling circuits 14, 22 when an aircraft equipped with the
system 10 is on the ground. For example, in the event of a failure
of one cooling circuit 14, 22, the cooling circuit 14, 22 which is
still functional can be used to ensure an emergency cooling of both
fuel cells 16, 24 until the operation of the fuel cell 16, 24,
supplied with cooling energy by the failed cooling circuit 14, 22,
has been properly ended.
[0042] By contrast, when an aircraft equipped with the system 10 is
in flight, in particular when it is cruising, only one of the two
fuel cells 16, 24 of the aircraft fuel cell system 12 is operated.
If no permanent thermal coupling is provided between the cooling
circuits 14, 22 of the cooling system 10, the thermal coupling of
the cooling circuits 14, 22 is then actively established, for
example by suitable control of corresponding valves. As a result,
it is possible to use both cooling circuits 14, 22 and therefore
both heat exchangers 20, 28 arranged in the cooling circuits 14, 22
for cooling the active fuel cell 16, 24, so that an effective and
efficient cooling of the active fuel cell 16, 24 can be realized.
In particular, the cooling capacity produced by the cooling ribs of
the heat exchangers 20, 28 is sufficient to ensure proper cooling
of the active fuel cell 16, 24. An additional flow of ambient air
through the first and/or the second heat exchanger 20, 28 can
therefore be dispensed with, as a result of which the aerodynamic
drag and therefore the fuel consumption of the aircraft equipped
with the system 10 for cooling an aircraft fuel cell system 12 can
be reduced. Finally, a freezing of the coolant in the cooling
circuit 14, 22 assigned to the inactive fuel cell 16, 22 is
prevented by the thermal coupling of the two cooling circuits 14,
22.
[0043] The system 10 for cooling an aircraft fuel cell system 12
shown in FIG. 2 differs from the arrangement according to FIG. 1 in
that the third heat exchanger 30, which ensures a thermal coupling
of the two cooling circuits 14, 22 of the cooling system 10, can be
additionally thermally coupled to a device to be heated. The device
to be heated is a fuel which flows through a fuel supply line 34
which connects a fuel tank 32 to the first and the second fuel cell
16, 24. The fuel tank 32 is configured in the form of a liquid
hydrogen tank which is adapted to store hydrogen in the liquid
state of matter. The hydrogen is supplied as fuel to the anodes of
the fuel cells 16, 24 of the aircraft fuel cell system 12. On
flowing through the third heat exchanger 30, the fuel stored in the
fuel tank 32 is heated up and optionally evaporated before being
supplied to the first and/or the second fuel cell 16, 24.
[0044] In principle, it is conceivable always to lead fuel, to be
supplied to the fuel cells 16, 24, through the third heat exchanger
30 and thereby establish a permanent thermal coupling of the device
to be heated to the third heat exchanger 30. Alternatively to this,
however, it is also possible to equip the system 10 with
corresponding valves and corresponding bypass lines which make it
possible to lead the fuel, flowing through the fuel supply line 34,
selectively either through the third heat exchanger 30 or past the
third heat exchanger 30. Such a configuration of the system 10
enables a merely temporary thermal coupling between the device to
be heated and the third heat exchanger 30.
[0045] As can be seen from FIG. 3, the third heat exchanger 30 is
embodied in the form of a tube-bundle heat exchanger, in which a
tube bundle which forms a section of the first cooling circuit 14
is connected in a heat-transferring manner to a tube bundle which
forms a section of the second cooling circuit 22. In particular,
tubes 36 assigned to the first cooling circuit 14 and tubes 38
assigned to the second cooling circuit 22 are connected to one
another in a thermally conducting manner in each case in pairs in
the third heat exchanger 30. For example, the tubes 36, 38 can be
soldered, adhesively bonded or welded to one another in pairs.
[0046] The tubes 36, 38 forming a section of the first cooling
circuit 14 and a section of the second cooling circuit 22 are
arranged in a receiving space 42 delimited by an outer casing 40 of
the third heat exchanger 30. During operation of the aircraft fuel
cell system 12, the fuel to be heated flows through the receiving
space 42, i.e., the receiving space 42 forms a section of the fuel
supply line 34 connecting the fuel tank 32 to the fuel cells 16,
24. As a result, a direct heat transfer is produced from the tubes
36, 38 forming a section of the first cooling circuit 14 and a
section of the second cooling circuit 22 to the fuel to be heated
flowing around the tubes 36, 38 in the receiving space 42.
[0047] In other respects, the structure and the functioning of the
system 10 for cooling an aircraft fuel cell system 12 illustrated
in FIG. 2 correspond to the structure and the functioning of the
arrangement according to FIG. 1.
[0048] As is apparent from the foregoing specification, the
invention is susceptible of being embodied with various alterations
and modifications which may differ particularly from those that
have been described in the preceding specification and description.
It should be understood that I wish to embody within the scope of
the patent warranted hereon all such modifications as reasonably
and properly come within the scope of my contribution to the
art.
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